Top sheet separating, hold-back-down mechanism

ABSTRACT

A sheet folding machine, especially one adapted to pick off and transfer successive fabric plies from a stack, is provided with improved sheet restraining means. It comprises a pneumatic separating means and a pair of cooperative hold-back and holddown devices for insuring that only single work pieces are cyclically removed from the stack.

5/1969 Szentkuti 271/26 R X "Milli/W; 1

United States Patent 1 1 1111 3,738,64 Gray et al. 1 1 June 12, 1973 TOP SHEET SEPARATING, 3,168,307 2/1965 Walton et al. 271/26 R HOLD BACK DOWN MECHANISM 1,705,506 3/1929 Spiess 271/27 75 l t R h d W G M bl h d P I 3,269,723 8/1966 Staines 271/27 1 men f zf gfig fg f fg hi FOREIGN PATENTS OR APPLICATIONS Jr, West Boxford, all f M 949,325 2/1964 Great Britain 271/26 [73] Assignee: USM Corporation, Boston, Mass. Primary Examiner Evon Bhmk 22 l N0 2 1971 Assistant Examiner-Bruce H. Stoner, Jr.

AItOrney Richard B. Megley, Vincent A. White and [21] Appl. No.. 202,145 Carl- E. Johnson [52] US. Cl ..27l/26,R, 271/14,

271 /104, 271/168 [57] P 51 1111.01 B6511 3/14 Sheet foldmg "1mm, espec'any one adapted to [58] Field of Search 271/26 R 30 31 plck off and transfer successive fabric plies from a 11 1 4 stack, is provided with improved sheet restraining means' It comprises a pneumatic separating means and [56] References Cited. a pair of cooperative, hold-back and hold-down devices for insuring that only single work pieces are cyclically UNITED STATES PATENTS removed from the stack. 3,442,505

10 Claims, 11 Drawing Figures PATENTEB 2 SKHZBF I Pmmenmzn 3.738.645

' SHEET 3 (If 4 PATENIED I 2 SHEEHHIF4 TOP SHEET SEPARATING, HOLD-BACK-DOWN MECHANISM Background of the Invention This invention relates to sheet feeding. More particularly, it is concerned with providing a machine for successively picking off and transferring to a predetermined position flexible, flat work pieces of fabric or the like. As herein used the term fabric is intended in a comprehensivesense and includes various woven and non-woven textiles, knit goods, and textile-like materials.

A wide variety of fabric handling and transferring machines have hitherto been available commercially. The great range of physically different sheet materials required to be processed has necessitated a variety of pick-off devices and controls therefore. In the fabric and garment industries, for example, wherein successive work pieces must be dealt with rapidly and with accurate positioning in relation to operating or treating stations, the problem of reliably and precisely moving and relocating work pieces one at a time from a stack has remained difficult. Factors such as limpness, compressibility, surface friction or adhesion, etc. which make manual handling of the material burdensome, also tend to mitigate against automatic machine handling reliability of individual work pieces.

An illustrative type of fabric handling machine which has enjoyed considerable commercial use is disclosed in U.S. Pat. No. 3,531,103 issued Sept. 29, 1970, in the name of R. W. Walton. It effectively employs one or more pick-off devices movable over a stack or work pieces to be singly transferred, a, blow-down device to facilitate release from the stack of its top ply, and a vac- V uum hold-back structure which is applied to a vertical edgesurface of the stack, the latter thereby being retained in its regular formation until the final ply is transferred. Another machine of this type is disclosed in U.S. Pat. No. 3,430,949 issued Mar. 4, 1969, in the name of Donald Herdeg et al.

An earlier fabric handling machine employing air flow and a baffle plate for attaining a fluttering in an exposed work piece to render the top ply removable is disclosed in U.S. Pat. No. 3,168,307 issued Feb. 2, 1965, in the name of R. W. Walton. Other approaches include-those disclosed, for instance, in U.S. Pat. No. 3,588,092 and No. 3,583,695.

SUMMARY OF THE INVENTION While a pick-off device can be expected with good reliability to seize and then move a piece of fabric from its stack, two incidental effects may often be incurred to adversely influence precision transfers thereafter of underlying sheets. Firstly, lateral transfer of a top ply may interfere with the proper position of an under ply by reason of frictional engagement therewith or due to its deformation or displacement by an air flow intended to assist separation of the top ply. Secondly, between interfaces of fibrous materials there often is an interlocking such that a second or underlying unwanted ply will at least partly cling to the exposed top ply which has been gripped for transfer. Irregular or indeterminate initial displacement of a work piece relative to the stack is inevitably reflected in the delivered position and this can produce poor quality or rejectable tions.

A main object of this invention accordingly is to provide, for use in an automatic fabric feeding machine, an improved fabric restraining means for eliminating inaccurate sheet delivery and/or the possibility of two or more fabric sheets being synchronously transferred.

Another object of this invention is to provide, in a machine having a pick-up device for transferring suc cessive single fabric work pieces from a stack, the combination of a separator, a hold-down, and a hold-back device operative to augment the reliability of the pickup device and avoid disturbing the position of the pieces remaining in the stack.

To these ends, and in accordance with a feature of the invention, there is provided in a machine adapted to feed sheets of fabric laterally from the top of a stack, a novel sheet control mechanism comprising a holdback, hold-down and ply separator device arranged to operate on the trailing margin of each ply about to be transferred. The device as herein shown includes a baffle or air foil partly extending heightwise over the stack and spaced from a pick-up means, and arranged to direct air flow unidirectionally outwardly on an upper surface of the top sheet to loosen and lift its marginal portion from the stack into proximity with the heightwise portion of the foil. As for the hold-down and retarder or hold back mechanisms, the hold-down mechanism is movable into clamping relation with a top nonseparatedwork piece of the stack, and the hold-back mechanism is concurrently movable into releasable work engaging relation with a side of the raised fabric margin and cooperative clamping relation with the heightwise portion of the foil or baffle. Accordingly, the arrangement is such that, the air flow now being reduced to just hold up a separated ply, only the top sheet engaged by the baffle may be cyclically removed by the pick-up means and its grip is enhanced by the drag or tensioning influence of the hold-back mechanism as the pick-off laterally transfers the separated single top piece of fabric.

In the illustrative embodiment the hold-back and hold-down mechanisms are cyclically movable laterally into a working position over the stack margin and then retract therefrom, the stack itself being bodily moved heightwise as necessary relative to the baffle and associated elements of the fabric restraining mechanism, for example, by known elevator means described in the above cited patents to Walton and Herdeg. The unidirectional air flow is preferably emitted at initially high and then low speed along the under surface of the baffle. The pick-off mechanism is preferably (though not necessarily) coupled to a vacuum source as also disclosed in the mentioned Walton patent. Optionally, a sensing device preferably also of a fluidic type is associated with the baffle for detecting when, for any reason, no top ply margin is separated from the stack. The sensing device provides a signal adapted either to terminate operation of the fabric feeder, or alternatively to cause the pick-off to recycle and thus insures continuous effective supply of single work pieces to an operating station.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects of the invention, together with various novel features and combinations of parts will now be more particularly described in connection with an illustrative embodiment and with reference to the accompanying drawings, in which:

FIG. 1 is a side elevation with portions broken away of an automatic fabric feeder of the general type shown in the U.S. Pat. No. 3,430,949 above mentioned, the machine incorporating the present invention to deliver only single work pieces to an adjacent station;

FIG. 2 is an enlarged view of top ply separating, holdback and hold-down mechanisms shown in FIG. 1, the parts being in inoperative positions;

FIG. 3 is an end view of the hold-back and hold-down mechanisms shown in FIG. 2 and as seen when looking to the right therein;

FIG. 4 is a plan view of the mechanism shown in FIGS. 2 and 3;

FIGS. 5-8 inclusive correspond to FIG. 2 and sequentially illustrate successive steps in the operation of the machine in removing a top work piece;

FIGS. 9 and 10 are similar to FIGS. 6 and 7, respectively, but illustrate the operation when, in addition to a top piece being separated from the stack, a second piece clings to the top piece; and

FIG. 11 is a perspective view of a sensor optionally associated with the ply separating means for controlling the machine.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to FIG. 1, a machine generally designated 12 for cyclically picking up successive pieces of flexible sheet material such as fabric work pieces P (FIGS. 5-10) in a stack S, is provided for effecting their transfer singly to a predetermined delivery point, for example exactly on the adjacent work station designated A in FIG. 1. The machine, conveniently for purposes of illustration, is assumed largely to correspond with that disclosed in the mentioned U.S. Pat. No. 3,430,949 except as hereinafter noted, though it will be apparent that the present invention is applicable in various types of fabric feeding equipment. The machine 12 comprises a frame 14, an overhead guide rail 16 supported thereby and extending generally in a direction from the stack S over the station A, and means including at least one pick-up device 18 reciprocably carried from a pick-up position over the stack S to a work release and delivery position adjacent to the station A. An elevator mechanism including a driven endless chain 20, for instance, is employed to control relative heightwise movement between the operating locality of the pickup device 18 and a horizontal work supporting table 22 and its stackholding pallet 24 thereon.

It will be understood that the pick-up device 18 may be of any suitable selected construction, and that means is provided for operating it transversely following engagement of its pick-up end with a fabric work piece P. A preferred device 18 has a plurality of pointed elements or teeth (not shown) usually biased angularly to prevent relative sliding movement in one direction with respect to the fabric, and may additionally employ a suctional draft to insure initial effective engagement of the pointed means with the single top ply P of fabric to be transferred.

Secured to the frame 14 by means of an upstanding stud 26 (FIGS. 2, 3) in a slotted slide 25 orthogonally secured to a cross slide 27 is an S-shaped bracket 28 (FIGS. 2-10) having a clamping collar portion 30 which may be angularly adjusted about the stud axis by means of a set screw 32. The bracket and slides serve adjustably to mount (as dictated by the contour of the stack S) a fabric restraining means with which this invention is particularly concerned, this means comprising in combination a top ply separator generally designated 34, a hold-back mechanism designated 36, and a hold-down mechanism 38. Construction of these elements will next be described, followed by an explanation of the manner of their cooperation.

The separating means 34 includes an air foil or baffle 40 (FIGS. 2, 4-10) in the form of a plate having its upper portion 42 fixedly secured to a later mentioned U-shaped bracket 44 which in turn is secured to the S- shaped bracket 28. The baffle 40 has a vertical portion 46, a horizontal portion 48 disposed only slightly above the level of the work engageable end of the pick-up l8 and laterally spaced therefrom on the side away from the delivery station A. Tangentially interconnecting the baffle portions 46, 48 is an arcuate work engageable surface portion 50 herein shown as of substantially constant radius of curvature. The portion 50 accordingly convexly extends over each successive top fabric ply designated P1 to be transferred by the pick-up 18 and is desirably disposed slightly inwardly of its trailing margin. When, as herein illustrated, a stack S has a vertical straight-aligned edge, the axis about which the surface 50 is substantially symmetric preferably extends parallel to that edge. The extent to which the surface 50 is inward of the extremity of the trailing margin is determined in part by the physical character of the fabric pieces to be transferred and their margin liftably as determined by a unidirectional air stream that is emitted from a nozzle 52 inserted in an outlet end of a tube 54 extending through the baffle portion 48. As shown in FIG. 5, the air flow is directed outwardly over the trailing margin of the ply P1 and generally parallel to the underside of the baffle portion 48. Initially, by control means not shown, the air flow is at higher speed to loosen the top ply from an underlying or second ply designated P2 therebeneath and cause the trailing margin of the ply P1 to be lifted from the stack. As the margin of the ply P1 is thus separated, the air flow is diminished to a level adequate, due to operation of the Bernouilli principle, to retain the trailing margin P1 in general contact with the convex surface of the baffle portion 50 and perhaps also with the vertical portion 46. More than one nozzle 52 may be employed usually in alignment for acting on the trailing margin if its extent so requires.

The hold-back mechanism 36 (FIG. 2) comprises a work clamp or retarder 56 disposed to engage the lifted trailing margin of the piece P1 and yieldingly urge it against the baffle 40. The retarder 56 is herein shown as comprising a pointed means such as card cloth 58 arcuately disposed on a holder 60 which is pivoted by v a pin 62 to the lower end of a lever 64. The upper end of the lever 64 is fulcrummed on the bracket 44, and the card cloth 58 is accordingly movable into and out of work restraining relation by means of a fluid pressure operated cylinder 66 having a piston rod 68 connected to the lever 64.

As herein illustrated, a permanent magnet 70 (FIGS. 2-10) serves as a portion of reset mechanism now to be explained and is secured as by a screw 72 to the lower end of the lever 64. When the retarder 56 is in its retracted or inoperative position as shown in FIG. 2, the lower portion of the holder 60 has been cammed relatively clockwise as seen in FIG. 5 about the pin 62 by a leaf spring 74, an upper portion of which is secured to the bracket 28. Thus an extension 76 of the holder 60 is moved into resetting or bridging engagement with the magnet 70. In subsequently moving the lever 64 clockwise the card cloth 58 is urged into hold-back relation with the relatively lifted trailing margin of the fabric P1 to yieldingly clamp the baffle 40 as shown in FIG. 6. Movement of the pick-up l8 laterally to transfer the fabric Pl as shown in FIG. 7 pivots the holder 60 counter-clockwise to release it from the magnet 70, the retarding hold-back influence of the card cloth 58 making more secure the engagement of the pick-up 18 with the fabric P1.

The hold-down mechanism 38 comprises a holddown lever 78 (FIGS. 2 and 3) pivotally secured by a pin 80 to a U-shaped bracket adjacent to the bracket 28. An upper end of the lever 78 is formed with a row of teeth 82 which, upon operation of a fluid pressure operated cylinder 84 having a piston rod 86 connected to the lever 78, are adapted to engage the margin of the top of the stack S after the ply P1 has been separated as above explained. The lever 78 is actuated into and out of operative position synchronously with the holdback mechanism 36. It will be understood that the teeth 82 may be pivotally controlled by detent mechanism (not shown) as a precaution to avoid damaging fabric.

FIGS. 5-8 inclusive illustrate the stages of operation of the separator means 34, the hold-back means 36, and the hold-down mechanism 38. When the pick-up 18 engages or is engaged by a leading portion of the top ply P1, the nozzle 52 directs a stream of air outwardly of the trailing margin of the fabric and parallel to the under surface of the baffle portion 48. This directed air circuitry to stop the machine until correction occurs, or if desired the signal may simply cause the pick-up means 18 to recycle until a top ply margin is properly lifted.

Assuming the trailing margin of the top ply P1 to have been separated, and the reduced air flow applied to cause that margin to closely cling to the baffle 40 (instead of fluttering as it may have when higher velocity air flowed, as indicated by the dash lines in FIG. 5) the hold-back device 36 releasably engages and restrains the margin against the baffle 40, and the holddown mechanism 38 simultaneously comes inwardly over and then descends to clamp the next top piece P2 on the stack S as shown in FIG. 6. Now the single top ply P1 is removed transversely away from the holdback and hold-down toward the station A by the pickup 18 as indicated in FIG. 7, tension in the fabric being increased by the yieldable drag imparted by the card cloth 58 until it is pivoted and the magnet 70 is forced to release the holder 60. This tension acting away from the direction in which work engaging points of the pick-up are oriented tends to insure their collectively attaining a more secure hold on the fabric being transferred thereby preventing its being dropped prior to proper delivery at station A. Pressure to the cylinders 66 and 84 now being relieved, their piston rods may be spring-returned and the parts are in their starting posiflow loosens the margin from the underlying ply P2 of i the stack and lifts the margin of the ply P1 into proximity with the under surface of the upwardly curved baffle portion 50. As shown in FIG. 6 this creates a restricted passage for the air flow between the portion 50 and the top surface of the trailing margin of the top piece PI. The induced Bernouilli effect then permits a reduction of air flow to maintain the lifter margin substantially in contact with the baffle 40.

Incidentally, there optionally may be provided a fluidic nozzle type sensor 90 (FIG. 11) associated with the baffle 40 for controlling recycling of the pick-up 18 and the fabric restraining mechanism described. The sensor 90 may be of a type responsive to suctional pressure flow or above atmospheric pressure flow. Thus the baffle may have an aperture or slot 92 for receiving the lower end of a feeler spring wire 94, the upper end of which is secured to a screw 96 threaded into the lever 64 and held in adjusted position by a nut 98. As shown in FIG. 2 the wire 94 is retracted from the slot 92 when the lever 64 is retracted to inoperative position. When normal operation occurs so that the separated top ply margin P1 engages a leaf spring 100 extending across the slot 92 as shown in FIG. 10, a pad 102 offset from the slot 92 and attached to the spring 100 will be slightly spaced from the sensing end of the sensor 90, and the machine 12 functions to remove and precisely deliver the top ply tothe station A. The spring 100 has one end fast on an extension of the bracket mounting the sensor 90 on the baffle 40. If for some reason the top ply margin failed to be separated and relatively raised from the stack sufficiently to engage the leaf spring 100, the advancing lower end of the wire 94 will not be blocked by the fabric P and will deflect the spring 100 and hence the pad 102 into contact or near contact with the sensor 90; this will signal the control tions for further cycling.

Referring to FIGS. 9 and 10, if the trailing margin of the under ply P2 clings to the top-most separated ply P1 as shown, the hold-back effect of the card cloth 58 will be exerted on the ply P2 contacted to retain it but not the ply P1. Then the transfer movement of the pick up 18 acting on the plyPl will withdraw it under tension from between the baffle 40 and the ply P2. The latter may then fall back into outspread top-most position on the stack S as the card cloth 58 progressively releases the ply P2, the hold-back mechanism 36 and the hold-down teeth 82 being retracted to their starting positions.

From the foregoing it will be clear that the invention provides a machine which is highly redundant in that: (1) if no fabric is fed, the machine will stop until the situation is corrected or recycle itself; (2) if one work piece is separated from the top of the stack that piece alone will be fed; and (3) if two or more pieces are separated from the top of the stack, only the top single piece will be fed by the pick-up 18.

Certain fabrics such as some stretchy knits are recog nized as being more apt to be easily damaged by stretching or abrasion. To avoid possibility of fabric damage in such situations, the present invention contemplates operation of the separating means and the hold-down means, but may eliminate operation of the hold back mechanism.

Having thus described our invention what we claim as new and desire to secure by Letters Patent of the United States is: I

1. A fabric feeding machine comprising means for supporting a stack of fabric work pieces to be transferred singly to a predetermined position, a pick-up device, mechanism for laterally moving the pick-up device between a pick-up position over the stack and a work release position adjacent to said predetermined position, and a work restraining mechanism for controlling the top and successive plies of the stack, the restraining mechanism comprising a separator means including a baffle disposed at least in part heightwise over the margin of the top ply remote from said predetermined position, mechanism for flowing air along the undersurface of said baffle to loosen and lift the top ply margin from the stack, and a hold-back means movable to restrain the lifted ply margin in cooperation with the baffle.

2. A fabric feeding machine comprising means for supporting a stack of fabric workpieces to be transferred singly to a predetermined position, a pick-up de vice, mechanism for laterally moving the pick-up device between a pick-up position over the stack and a work release position adjacent to said predetermined position, and a work restraining mechanism for controlling the top and successive plies of the stack, the restraining mechanism comprising a separator means including a baffle, disposed at least in part heightwise over the margin of the top ply remote from said predetermined position, the baffle including a flat portion substantially parallel to the top ply and an arcuate portion extending heightwise thereof, mechanism for flowing air along the undersurface of said baffle to loosen and lift the top ply margin from the stack, the mechanism for flowing air being adapted initially to direct a higher air speed flow along the undersurface of said flat portion and over the top ply margin and away from the pick-up device, and then a lowered speed air flow to lift the loosened top ply margin into proximity with said arcuate portion of the baffle, a hold-back means movable to restrain the lifted ply margin in cooperation with the baffle, and control mechanism operable to move the hold-back into work restraining relation to the baffle when the lower speed air flow is operating.

3. A fabric feeding machine comprising means for supporting a stack of fabric workpieces to be transferred singly to a predetermined position, a pick-up device, mechanism for laterally moving the pick-up device between the pick-up position over the stack and a work release position adjacent to said predetermined position, a work restraining mechanism for controlling the top and successive plies of the stack, the restraining mechanism comprising a separator means including a baffle disposed in part heightwise over the margin of the top ply remote from said predetermined position, mechanism for flowing air along the undersurface of said baffle to loosen and lift the top ply margin from the stack, a hold-back means movable to restrain the lifted ply margin in cooperation with the baffle, a sensor associated with the baffle in its heightwise extending portion and responsive to the presence of the margin of a fabric ply lifted adjacent thereto and a control means including the sensor for discontinuing operation of the machine cycle when the sensor fails to signal the presence of the lifted margin.

4. For use in a machine having a pick-up device movable for feeding successive fabric plies singly from the top of the stack and delivering them to a predetermined position, mechanism operable to restrain the margin of the successive plies on the opposite side of the device from said predetermined position, said mechanism including in combination a baffle extending from near the top of the stack and outwardly heightwise thereof over said margin, means for flowing air outwardly of the stack and along the adjacent surface of the baffle to loosen and relatively lift the top ply margin substantially into contact therewith, a hold-back device mounted to move into cooperative work restraining relation with the baffle, the hold-back device including a plurality of pointed work-engageable elements, a movable holder for convexly disposing the pointed elements, and mechanism for causing the holder to move said elements yieldingly into work clamping relation against the baffle each time theair flow has lifted a fabric margin thereagainst, and mechanism for operating the margin restraining mechanism as the pick-up device is about to transfer the top ply from a stack.

5. Mechanism as set forth in claim 4 wherein the hold-back device further includes a movable support for pivotally mounting said holder, mechanism for cyclically moving the support to carry the holder between an inoperative out-of-the-way position and an operative position over the stack, and means associated with the support for releasably retaining the holder in selected angular relation thereon.

6. Mechanism as set forth in claim 5 wherein the means for releasably retaining the holder is a magnet secured to the support, and a reset cam is disposed to restore the holder into engagement with the magnet when the attractive force of the latter has been overcome by the pick-up device in tensioning and transferring a fabric ply from said pointed elements.

7. In a machine having a reciprocable pick-up device adapted to deliver successive fabric sheets from the top of a stack to a delivery position, a baffle disposed over the margin of the stack on the opposite side of the pickup from the delivery position, a nozzle disposed between the baffle and a top sheet of the stack for directing a stream of air outwardly over the margin of the top ply of the stack and lifting said top ply margin against the baffle, a hold-back means for yieldingly restraining the lifted top ply margin and any second ply margin clinging thereto cooperatively with the baffle against tension imparted by the pick-up device, the hold-back means including a biased pointed means mounted for relative fabric clamping movement with respect to the portion of the baffle extending upwardly from the stack, a retarder means acting on the pointed means to cause it to tension the fabric being seized by the pickup device until a predetermined tension is reached, and a hold-down means for clamping the fabric sheets remaining in the stack. 7

8. A machine as set forth in claim 7 wherein the pointed means is adapted to contact and retain only the ply contacted thereby.

9. A machine as set forth in claim 7 wherein the retarder means for controlling said predetermined tension in the fabric is a magnet.

10. A machine as set forth in claim 7 wherein the baffle is formed with a slot disposed to be covered by a portion of the lifted margin of the top ply, a sensing mechanism is disposed adjacent to said slot, and a control member receivable in the slot in the absence of the top ply margin being raised to cover the slot is effective to cause the sensing mechanism to discontinue or recycle operation of the machine.

a m ,s a a aggy UNITED STATES PATENT OFFICE I i.

QERTIFICATE: CORRECTION Patent No. 37384645 i Dated June 12 1973 J lnventofls) Richard W. Gray, Paul Rumball, Oliver C.Brett,Jr.

It is certified that error appears in the above-identified peteht and that said Letters Patent are hereby corrected as shown below:

In the Abstract I I Line I, after sheet, before machine, delete folding and insert -feeding- Signed and sealed this 12th 531;; "or MaTCh lQYL I (SEAL) it A Attest zf f Cemmissioine of Patents 

1. A fabric feeding machine comprising means for supporting a stack of fabric work pieces to be transferred singly to a predetermined position, a pick-up device, mechanism for laterally moving the pick-up device between a pick-up position over the stack and a work release position adjacent to said predetermined position, and a work restraining mechanism for controlling the top and successive plies of the stack, the restraining mechanism comprising a separator means including a baffle disposed at least in part heightwise over the margin of the top ply remote from said predetermined position, mechanism for flowing air along the undersurface of said baffle to loosen and lift the top ply margin from the stack, and a hold-back means movable to restrain the lifted ply margin in cooperation with the baffle.
 2. A fabric feeding machine comprising means for supporting a stack of fabric workpieces to be transferred singly to a predetermined position, a pick-up device, mechanism for laterally moving the pick-up device between a pick-up position over the stack and a work release position adjacent to said predetermined position, and a work restraining mechanism for controlling the top and successive plies of the stack, the restraining mechanism comprising a separator means including a baffle, disposed at least in part heightwise over the margin of the top ply remote from said predetermined position, the baffle including a flat portion substantially parallel to the top ply and an arcuate portion extending heightwise thereof, mechanism for flowing air along the undersurface of said baffle to loosen and lift the top ply margin from the stack, the mechanism for flowing air being adapted initially to direct a higher air speed flow along the undersurface of said flat portion and over the top ply margin and away from the pick-up device, and then a lowered speed air flow to lift the loosened top ply margin into proximity with said arcuate portion of the baffle, a hold-back means movable to restrain the lifted ply margin in cooperation with the baffle, and control mechanism operable to move the hold-back into work restraining relation to the baffle when the lower speed air flow is operating.
 3. A fabric feeding machine comprising means for supporting a stack of fabric workpieces to be transferred singly to a predetermined position, a pick-up device, mechanism for laterally moving the pick-up device between the pick-up position over the stack and a work release position adjacent to said predetermined position, a work restraining mechanism for controlling the top and successive plies of the stack, the restraining mechanism comprising a separator means including a baffle disposed in part heightwise over the margin of the top ply remote from said predetermined position, mechanism for flowing air along the undersurface of said baffle to loosen and lift the top ply margin from the stack, a hold-back means movable to restrain the lifted ply margin in cooperation with the baffle, a sensor associated with the baffle in its heightwise extending portion and responsive to the presence of the margin of a fabric ply lifted adjacent thereto and a control means including the sensor for discontinuing operation of the machine cycle when the sensor fails to signal the presence of the lifted margin.
 4. For use in a machine having a pick-up device movable for feeding successive fabric plies singly from the top of the stack and delivering them to a predetermined position, mechanism operable to restrain the margin of the successive plies on the opposite side of the device from said predetermined position, said mechanism including in combination a baffle extending from near the top of the stack and outwardly heightwise thereof over said margin, means for flowing air outwardly of the stack and along the adjacent surface of the baffle to loosen and relatively lift the top ply margin substantially into contact therewith, a hold-back device mounted to move into cooperative work restraining relation with the baffle, the hold-back device including a plurality of pointed work-engageable elements, a movable holder for convexly disposing the pointed elements, and mechanism for causing the holder to move said elements yieldingly into work clamping relation against the baffle each time the air flow has lifted a fabric margin thereagainst, and mechanism for operating the margin restraining mechanism as the pick-up device is about to transfer the top ply from a stack.
 5. Mechanism as set forth in claim 4 wherein the hold-back device further includes a movable support for pivotally mounting said holder, mechanism for cyclically moving the support to carry the holder between an inoperative out-of-the-way position and an operative position over the stack, and means associated with the support for releasably retaining the holder in selected angular relation thereon.
 6. Mechanism as set forth in claim 5 wherein the means for releasably retaining the holder is a magnet secured to the support, and a reset cam is disposed to restore the holder into engagement with the magnet when the attractive force of the latter has been overcome by the pick-up device in tensioning and transferring a fabric ply from said pointed elements.
 7. In a machine having a reciprocable pick-up device adapted to deliver successive fabric sheets from the top of a stack to a delivery position, a baffle disposed over the margin of the stack on the opposite side of the pick-up from the delivery position, a nozzle disposed between the baffle and a top sheet of the stack for directing a stream of air outwardly over the margin of the top ply of the stack and lifting said top ply margin against the baffle, a hold-back means for yieldingly restraining the lifted top ply margin and any second ply margin clinging thereto cooperatively with the baffle against tension imparted by the pick-up device, the hold-back means including a biased pointed means mounted for relative fabric clamping movement with respect to the portion of the baffle extending upwardly from the stack, a retarder means acting on the pointed means to cause it to tension the fabric being seized by the pick-up device until a predetermined tension is reached, and a hold-down means for clamping the fabric sheets remaining in the stack.
 8. A machine as set forth in claim 7 wherein the pointed means is adapted to contact and retain only the ply contacted thereby.
 9. A machine as set forth in claim 7 wherein the retarder means for controlling said predetermined tension in the fabric Is a magnet.
 10. A machine as set forth in claim 7 wherein the baffle is formed with a slot disposed to be covered by a portion of the lifted margin of the top ply, a sensing mechanism is disposed adjacent to said slot, and a control member receivable in the slot in the absence of the top ply margin being raised to cover the slot is effective to cause the sensing mechanism to discontinue or recycle operation of the machine. 